The present invention relates to a method of manufacturing a semiconductor integrated circuit device. More particularly, the present invention relates to a technique that is applicable to a semiconductor integrated circuit device in which two or more types of MISFETs (Metal Insulator Semiconductor Field Effect Transistors) have gate insulating films that are mutually different in thickness and are formed on the same semiconductor substrate.
The operating voltage of a semiconductor device has been reduced generation by generation in the development of semiconductor integrated circuits for achieving higher integration and a lower power consumption. Under such circumstances, a MISFET is reduced in size in accordance with a scaling law for maintaining and improving the device performance, so that the thickness of the gate insulating film is reduced at the same time. However, for example, with a CMOS logic LSI, or the like, the operating voltage is different between the internal circuit and the input/output circuit. For this reason, a MISFET in which the thickness of the gate insulating film is relatively larger is also required.
For such a reason, in a recent semiconductor device, efforts have been pursued to effect the introduction of a process of forming a plurality of types of MISFETs which have gate insulating films that are mutually different in thickness on the same substrate. For example, Japanese Published Unexamined Patent Application No. 2000-188338 discloses a process of separately forming a gate insulating film made of silicon dioxide in a first region of a semiconductor substrate and another gate insulating film made of silicon nitride or tantalum oxide in a second region thereof.
For example, a MISFET with a gate length of not more than 0.2xcexcm is required to have a gate insulating film having a small thickness of around 3 nm in terms of a silicon dioxide film. However, if the thickness of the gate insulating film using a silicon dioxide film is reduced down to about 3 nm, the direct tunneling current flowing through the gate insulating film increases, so that a gate leakage current at a level that is not negligible from the viewpoint of reducing the power consumption is generated. Therefore, a MISFET in which the gate insulating film is comprised of silicon dioxide imposes a limitation on the increase in gate insulating film capacitance for improving the current driving ability.
A conceivable alternative as a countermeasure to this problem is to increase the physical film thickness of the gate insulating film by using a high dielectric film of titanium dioxide (TiO2), hafnium dioxide (HfO2), or the like, which has a larger relative dielectric constant than that of silicon nitride.
Thus, for a semiconductor device in which MISFETs having gate insulating films that are mutually different in thickness are formed on the same substrate, a process of forming a part of the gate insulating film with a high dielectric film and forming another part thereof with a silicon dioxide film is required. However, with the foregoing semiconductor device manufacturing method, the surface of the semiconductor substrate is exposed to air between the time when the semiconductor substrate surface has been exposed and the time when a gate insulating film made of silicon nitride or tantalum oxide is formed. Accordingly, impurities (foreign matter), such as carbon (C) contained in the air, are deposited on the semiconductor substrate surface, unfavorably resulting in a reduction in the withstand voltage of the gate insulating film deposited thereon.
Further, by exposure of the semiconductor substrate surface to air, a natural oxide film is formed on the semiconductor substrate surface. Even if a high dielectric film is deposited thereon to form a gate insulating film, the gate insulating film capacitance is reduced. As a consequence, it becomes difficult to implement a high-performance MISFET having a high current driving ability.
It is an object of the present invention to provide a technique, in a process of forming a MISFET having a gate insulating film comprised of a high dielectric film on a semiconductor substrate, for suppressing the formation of an undesirable natural oxide film at the interface between the semiconductor substrate and the gate insulating film.
It is another object of the present invention to provide a technique, in a process of forming a MISFET having a gate insulating film comprised of a high dielectric film on a semiconductor substrate, for improving the withstand voltage of the gate insulating film.
The above and other objects and novel features of the present invention will be apparent from the following description in this specification and the accompanying drawings.
Out of the many aspects of the present invention disclosed in this application, a general outline of typical ones will be briefly described as follows.
A method of manufacturing a semiconductor integrated circuit device in accordance with the present invention, using a high dielectric film for a gate insulating film, includes: a step of removing a silicon dioxide film on the semiconductor substrate surface; a step of cleaning the semiconductor substrate surface; and a step of depositing a high dielectric film on the semiconductor substrate surface. With this method, the semiconductor substrate is held in an inert atmosphere between the time when the semiconductor substrate surface has been cleaned and when the high dielectric film is deposited. As a consequence, it is possible to prevent a reduction in the withstand voltage of the gate insulating film, and it is possible to improve the current driving ability by preventing the reduction in capacitance of the gate insulating film.
A method of manufacturing a semiconductor integrated circuit device in accordance with the present invention, includes the steps of: (a) preparing a silicon substrate having a first region and a second region on a principal surface; (b) removing a film including a natural oxide film formed on the principal surface of the silicon substrate, and thereby exposing a silicon layer on the principal surface of the silicon substrate; (c) forming, after the step (b), a first insulating film having a smaller relative dielectric constant than that of a silicon nitride film on the silicon layer; (d) selectively removing the first insulating film in the second region, leaving the first insulating film in the first region, and thereby exposing the silicon layer in the second region; (e) forming, after the step (d), a second insulating film having a larger relative dielectric constant than that of a silicon nitride film on the first insulating film in the first region and on the silicon layer in the second region; (f) forming a first conductive layer on the second insulating film; and (g) patterning the first conductive layer, and thereby forming a gate electrode of a first MISFET comprised of the first conductive layer on the second insulating film in the first region and forming a gate electrode of a second MISFET comprised of the first conductive layer on the second insulating film in the second region, wherein at least the steps (b) to (e) are continuously carried out without exposing the silicon substrate to air.